MRI is a noninvasive imaging technique that provides clinicians and diagnosticians with information regarding anatomical structures and statuses of a region of interest inside a patient's body.
Generally, MRI is applied to imaging of an examination area where a patient to be examined is located with an almost uniform main magnetic field B0. A magnetic dipole, which is selected in the patient by exciting and operating a radio frequency (RF) magnetic field B1 (if not, it is arranged parallel with the main magnetic field), is excited and inclined by the magnetic resonance. The resonance is controlled to induce a detectable magnetic resonance echo signals from the selected region of the patient. The spatially encoded echo signal is formed by applied gradient fields. A raw data transmitted from an MRI scanner has frequency information and is collected in a 2- or 3-dimensional matrix form of a frequency region which is known as a k-space. The patient's images are reconstructed from the frequency data through the 2D or 3D inverse Fourier transform, or the other well-known reconstruction techniques.
MR imaging of the related art generates a data volume consisting of voxels with 3D features. Sizes of the voxels are decided by physical features of the MRI scanner as well as user's settings.
Recently, 3D information is used for creating diagnosis and treatment. This is why 2D images in blood vessel images simply show thin slides of a blood vessel and make it difficult to diagnose stenosis or other disorders, for example.
In general, a 3D image is obtained by piling the 2D images, which are combined in order to create a volume image, or by using 3D image-acquiring techniques.
If the voxel volume is decreased, the MR image has a characteristic of a decreased signal-to-noise ratio. Therefore, there is a problem that a high resolution 3D image has a restricted resolution due to the signal-to-noise ratio.
FIG. 1 shows an example for explaining a general method for reconstructing 3D MR images of the related art.
The method for reconstructing 3D images by using MRI of the related art reconstructs the 3D images by exciting the region of interest, obtaining 3D frequency information, and performing the inverse Fourier transform.
However, referring to FIG. 1, slice images at beginning and end portions of the region of interest may show aliasing artifacts, which are images blurred or contaminated due to mixing of images outside the region of interest.
Since a truncated radio frequency pulse is commonly used in MRI, it is difficult to completely obtain signals of the preferred region of interest only. Therefore, a part outside the region of interest is excited, signals of the undesired part are added, and thus the aliasing artifacts are occurred. In addition, there is a problem to cause a field inhomogeneity artifact B0 that the signals of the region of interest are distorted and move to other regions due to non-uniformity of the main magnetic field caused by the magnetic property inside a human body.